Genetics Final

Genetics

Branch of biology concerned with the study of inheritance and variation of biological traits

Biological traits

controlled by genes contained within the genetic material

Genes

discrete information carrying units of heredity that control or contribute to biological traits

Monogenic traits

traits controlled by a single gene

Oligogenic traits

traits controlled by several genes

polygenic traits

traits controlled by combination of genes and environmental factors

karyotype

Overview of all chromosomes in an animal, the human has 23 pairs and 46 total chromosomes in it

Chromosomes

tightly packed DNA, containing genes, single double-stranded DNA is tightly coiled around discrete evenly spaced nucleosomes (consisting of 8 histone proteins)

Prokaryotic cell

lacks a true nucleus and other membrane-enclosed organelles, simpler in internal structure, include bacteria and archea

Eukaryotic cell

has nucleus, membrane bound organelles, more complex, includes animal and plants, larger than other type of cell

Viruses

made up of DNA and RNA, enclosed in a protein coat (capsid) and sometimes further wrapped in a membranous envelope

Hippocrates

~400 BC, found out that male contributions to offspring carried in semen, and similar contributions from female

Aristotle

~320 BC, all inheritance comes from males and females supply the parts from which offspring are made

Hindu Religion

~1000 AD, thought that sick parents would often pass the sickness on to offspring

Charles Darwin

~1859, published origin of species by means of natural selection

Gregor mendel

1866, published experiments on inheritance with pea plants, father of genetics

Friedrich Miescher

1869, isolated nuclein (nucleic acid (DNA)), form nuclei of white blood cells

Walther Flemming

1879, identified chromatin in cell nuclei and links it to chromosomes and cell division

Thomas Hunt morgan

1910, demonstrated that genes are located of specific chromosomes

Oswald Avery, Colin Macleod, and Maclyn McCarty

1944, Demonstrated that DNA is the genetic material

Watson and Crick

1953, figured out the 3D structure of DNA and hypothesized a mechanism for DNA replication

Rosalind Franklin

1952, generated X-ray crystallography data that was crucial to Watson and cricks 3D model of DNA

Frederick Sanger

1977, developed the chain termination method for DNA sequencing

Kary Mullis

1983, Invented the polymerase chain reaction (PCR) used to amplify DNA molecules

Diploid

Human somatic cells, 2n, in pairs (2(23) =46)

Haploid

Human gametes, n, not in pairs (23)

Genome

full complement of genetic material of an organism, somatic cell (6.4×10^9 BP and 16,000 mito BP) Gamete Cell (3.2×10^9 BP and 16,000 mito BP) BUT same number of GENES

Cattle

Diploid: 60, Haploid: 30

Sheep

Diploid: 54, Haploid: 27

Pig

Diploid: 38, Haploid: 19

Horse

Diploid: 64, Haploid: 32

Goat

Diploid: 60, Haploid: 30

Chicken

Diploid: 78, haploid: 39

Mitosis

Gives rise to two genetically identical daughter nuclei, it is a part of the cell cycle and when coupled with cytokinesis it functions in reproduction, growth and tissue repair, diploid chromosome number is always maintained

Cytokenesis

division of the cytolplasm

Functions of Mitosis

Asexual reproduction, growth and development, tissue renewal

Coenocyte

multinucleated cell generated from multiple nuclear divisions without cytokinesis, also known as a syncytium

Cell division phases

Interphase: G1, S, G2 and Mitotic phase: mitosis and cytokinesis

G1 Phase

metabolic activity and growth,

S phase

Metabolic activity, growth and DNA synthesis (replication)

G2 phase

metabolic activity, growth, and preparation for cell division

Mitosis Phases

Prophase, prometaphase, metaphase, anaphase, and telophase

Prophase

DNA condenses into chromosomes, duplicated chromosomes appear as sister chromatids joined at a centromere

Prometaphase

chromosomes are even more condensed, kinetochore formed on chromosomes and microtubules will attach and start to move chromosomes

Metaphase

sister chromatids align along the metaphase plate

Anaphase

Sister chromatids separate to each side of the cell

Telophase

along with cytokinesis is the generation of two daughter cells

Meiosis

two-step form of cell division in sexually reproducing organisms that results in the formation of haploid gametes from diploid parent cells

Meiosis 1

Homologs are separated and 2 daughter cells are created (diploid), same 4 phases (prophase, metaphase, anaphase, telophase), where crossing over happens

Meiosis 2

Sister chromatids are separated and 4 daughter cells are created (haploid), same 4 phases (prophase, metaphase, anaphase, telophase)

3 main processes creating genetic diversity

• independent assortment of chromosomes into gametes

• crossing-over giving rise to genetic recombination

• random fertilization of male and female gametes

possible chromosome combinations

2^n, n=haploid number of chromosomes, ex: horse n=32 so 2³² = 4.3 billion possible combinations

Crossing over

involves the exchange of chromosomal segments between non-sister chromatids, produces chromosomes that are different from parental chromosomes, a precise gene by gene process, important for genetic variation, takes place in prophase 1

Chiasmata

physical points of contact between non-sister chromatids in a tetrad

Where did Mendel do his work?

St. Thomas Abbey in east Czech Republic

Pea Plants

mendels choice of organism for experiments, because it has a short life cycle, has large numbers of offspring, many different strains, self pollinating and can cross pollinate, easy to track either or characters (7)

Pea plant characters

height, flower color, flower position, seed color, seed shape, pod color and pod shape

Monohybrid cross

involved analysis of only one character

Blending inheritance

Mendels 1st hypothesis, where the traits of the two parents would blend together in the offspring, this would produce uniformity in traits

Particulate inheritance

2nd hypothesis by Mendel, where parents pass on discrete heritable units to offspring, they would retain their own identity in offspring, one or the other

mendels 1st law

law of segregation

Law of segregation

two alleles of a gene controlling a character separate into different gametes during gamete production, such that half of the gametes carry one allele and the other half carry the other allele

Genes

located on chromosomes

Alleles

alternative versions of a gene, can be dominant or recessive

Locus

position of a gene on a chromosome

Mendels 2nd law

law of independent Assortment

Law of Independent Assortment

Mendel discovered this using test crosses involving two characters, the alleles of two different traits will be segregated independently of each other and not together (i.e. seed color and seed shape are independent of each other)

Multiplication rule

probability rule, if there is 50% chance of R and 50% chance of r then there is a 25% chance of getting Rr (0.5 × 0.5 =0.25)

William C. Farabee

1903, he documented brachydactyly, the first Mendelian trait described in humans and shoed it had an autosomal dominant pattern of inheritance

CFTR gene

causes cystic fibrosis, mutation in the CF transmembrane conductance regulator gene

HBB gene

Causes sickle cell anemia, because of a mutation in the human beta globin gene

Ability to taste PTC

due to a polymorphism in the TAS2R38 gene

Pseudoachrondroplasiais

caused by inactivating mutations in the cartilage oligomeric matrix protein gene (COMP), DD genotype are thought to produce a lethal outcome during embryonic development

25%

Tom and marry are carriers (Aa) for a recessive condition, what is the probably that their first child will be affected by the condition (aa)?

6.25% (0.25 × 0.25)

Tom and marry are carriers (Aa) for a recessive condition. What is the probability that their two children will both be affected by the condition (aa)?

56.25% (0.75 × 0.75)

Tom and marry are carriers (Aa) for a recessive condition. What is the probability that their two children will not be affected by the condition?

37.5% (0.25 × 0.75) + (0.25 × 0.75)

Tom and marry are carriers (Aa) for a recessive condition. What is the probability that only one of their children will be affected by the condition?

Pleiotropy

if a gene affects multiple phenotypes

Incomplete dominance

phenotype of heterozygote is distinct and often intermediate to the phenotype of either homozygote, (red RR, pink Rw, white ww)

Codominance

the phenotypic affect of both alleles is evident in the heterozygote, i.e. blood type, and roan coat color in cattle

Lethal alleles

individuals with two lethal alleles will not survive, can be dominant or recessive. i.e. overall lethal white foal syndrome in horses, and new mutations that are dominant can also produce lethaility

Epistasis

when a gene alters the phenotypic expression of another gene at a different genetic locus, coat color in labs

Complex traits

also called quantitative, polygenic or multifactorial, are traits determined by genomic variation at many genes, regulatory elements, and multiple environmental factors, such has height, and BMI in humans, fleece weight in sheep, milk yield in dairy cattle, and more

SBE1 gene recessivity

in pea plants if the SBE1 gene is recessive, the pea plants cannot make amylopectin from amylose, leading to wrinkled shape, but if there is one copy of the dominant gene then the seed will not appear wrinkled at all because it can product amyplopectin

Universal Donor

Blood type O

Universal Recipient

Blood type AB

Naming Genes

agree can gene (ACAN) on bovine chromosome 21 would be named as, Bovine Taurus chromosome 21, Gene = BTA21

Polled Intersex Syndrome

PIS, absence of horns (polled), and has evidence of both genetailia (intersex), affects the genes KCNJ15, ERG on the CHI1

Uniform environment

impacts heritability, more uniform = more heritable the trait is

Thomas Hunt Morgan

Discovered first solid evidence of associating a specific gene with a specific chromosome in 1900s, he worked on fruit flies

1909-1911

Morgans experiments with the flies demonstrated Mendels genes are located on chromosomes

1915

Morgan published “the mechanism of mendelian heredity”

1933

Morgan was awarded the Nobel prize in physiology or medicine

Why fruit flies?

Prolific breeders, new generation can be bred every two weeks, only have four pairs of chromosomes, three pairs of autosomes and one pair of sex chromosomes, normal and most common phenotype was wild type (WT)

Pseudoautosomal regions

PARS, regions for sex chromosomes that can pair up and separate during meiosis

Homogametic sex

female mammals (XX), male birds (ZZ)

Heterogametic sex

Male mammals (XY) and female birds (ZW)

Transcription factor proteins

regulate genes by allowing increased transcription or stopping and slowing transcription

MSY

male specific portion of the Y chromosome

Hemizygous

used when describing X sex-linked genes for males